(PP502) Comparison of Auditory Brain-Stem Responses Elicited with Tone-Bursts and NB Chirp Stimuli in Adults

There is a growing interest in the use of Narrow Band (NB) chirp stimuli to obtain ABRs for threshold estimation as they produce robust responses. The aim of our study is to compare ABRs elicited with tone bursts and NB chirps (developed by Claus Elberling, abbreviated CE, and available in the Interacoustics EP25) to behavioral thresholds in adult participants with normal hearing sensitivity and sensory hearing loss. ABRs will be elicited with tone bursts at 500 and 2000 Hz and with NB, level-specific CE chirps centered around those same frequencies. Correction factors to obtain eHL from nHL will be shared.

 

Summary: 

Rationale/ Purpose

It is important to study the relationship between behavioral thresholds and ABR thresholds in order to estimate hearing sensitivity in clinical populations. Narrow Band (NB) chirps developed by Claus Elberling (CE) are octave-band chirps which compensate for cochlear travel time and produce robust wave V responses. We hypothesize that ABR wave V thresholds obtained with NB CE Chirps will be closer to behavioral thresholds compared with ABR thresholds obtained with tone bursts. We will test normal hearing adults and those with mild to moderate sensory loss to explore the correlations between ABR wave V and behavioral thresholds.

Methods

A total of 24 participants will be tested, with 12 participants in each group: one with normal hearing sensitivity and the other with hearing loss. In this study, we will focus on testing at 500 and 2000 Hz only. Pure tone audiometry will be used to obtain behavioral thresholds. ABRs will be obtained with rarefaction, 2-1-2 tone bursts at 500 and 2000 Hz, and NB CE-Chirps with center frequencies at 500 and 2000 Hz. We will begin testing at 80 dBnHL in normal hearing individuals and 90 dBnHL in those with mild to moderately severe sensorineural hearing loss individuals and descend. A bracketing procedure of “down 10 dB, up 5 dB” will be used close to threshold. Both types of stimuli will be presented at a rate of 21.1/sec. ABRs will be recorded using a conventional, single-channel electrode montage. The filter setting will be 33 Hz-3000 Hz and an average of at least 2000 sweeps will be obtained. All data will be obtained with participants in a quiet state or asleep. Statistical analysis will include regression tests of behavioral and ABR thresholds. 

Results

We are close to completion of testing normal hearing participants. We expect to have all data collected by February 2022. Preliminary results obtained in participants with normal hearing show comparable wave V amplitudes with the 500 Hz NB CE chirp and 500 Hz tone bursts at the highest intensity (80 dB nHL). Wave V thresholds with NB CE Chirps were on average 10 dB lower than wave V thresholds with tone bursts. Additionally, wave V thresholds with NB chirps were on average 13 dB greater than behavioral thresholds at 500 Hz. A similar pattern of responses is seen with 2000 Hz tone bursts ABRs and the NB CE Chirp ABR centered at that frequency. The exception being that wave V thresholds with 2000 Hz NB CE chirps were on average 10 dB greater than the behavioral thresholds at that frequency.  

Conclusions and importance of work

The results of this project will be used to generate normative data for ABRs with NB CE chirps and tone bursts for use in the clinic. Data obtained from the two groups will provide guidelines for interpretation of NB CE chirp ABRs in the presence of hearing loss. These results will be invaluable in estimation of hearing thresholds in difficult-to-test individuals (for example, those who may be malingering or are unable to respond due to cognitive limitations).